(1) Field of the Invention
The present invention pertains to an adjustable weight system for a rotor blade of a rotary wing aircraft. Specifically, the present invention pertains to an adjustable weight system for a helicopter rotor blade, where the trailing edge of the rotor blade is formed with a plurality of recesses that each receive an aerodynamically shaped weight to adjust and balance the weight of the rotor blade.
(2) Description of the Related Art
For rotary wing aircraft, for example helicopters, it is necessary that the rotor blades of the aircraft have a mass balance adjustment capability at the tip end or distal end of each rotor blade. Balancing the weight of a rotor blade enables a set of the balanced rotor blades to be operated with reduced vibration. The mass balance adjustment of the rotor blade is provided for both the spanwise direction, i.e. the longitudinal length of the rotor blade, and the chordwise direction, i.e. the lateral width of the rotor blade. This is typically achieved by a helicopter rotor blade balance system that has a pair of adjustable weights positioned adjacent the leading edge of the rotor blade and the distal end of the rotor blade. The two adjustable weights are spaced from each other in the chordwise or lateral direction on the rotor blade. The weights are positioned in a pair of mechanical pockets provided in the surface of the rotor blade. The pockets are typically constructed of metal to withstand the load created by the weights contained in the pockets and to transfer the load to the rotor blade structure.
A typical construction of a prior art rotor blade mass balance system is shown in FIG. 1. FIG. 1 shows a section of a rotor blade 10 adjacent the blade distal end. A first forward pocket 12 is positioned in a complementary shaped cavity in the rotor blade adjacent the blade leading edge 14, and a second forward pocket 16 is positioned in a complementary shaped cavity in the rotor blade adjacent the first forward pocket 12. The first pocket 12 and second pocket 16 are typically secured to the rotor blade structural spar tube 22. This positioning of the pair of pockets 12,16 provides sufficient structural strength to the pockets in the blade.
A pair of weights 24, 26 are positioned in the pockets 12, 16 in adjusting the mass balance of the rotor blade. The weights 24, 26 are secured in the pockets 12, 16 by a plurality of mechanical fasteners 28, for example, self-locking screws. A cover plate 32 is provided to cover over the pair of weights 24, 26. The cover plate 32 fits into a complementary shaped recess 34 in the surface of the blade 10. A plurality of mechanical fasteners 36, for example self-locking screws, are provided to secure the cover plate 32 to the surface of the blade 10.
The above described mass balancing system of the prior art is disadvantaged in that the two weight pockets 12, 16 cannot be spaced any further apart in the chordwise or lateral direction of the blade 10 beyond the lateral width of the rotor blade spar tube 22. The structure of the tube 22 is needed to secure the pockets 12, 16 and weights 24, 26 in the rotor blade 10. The portion of the rotor blade 10 that extends aft of the spar tube 22 is typically constructed of lightweight composite material skins or layers that extend over the opposite sides of a core material of the blade. This portion of the blade is typically configured and dimensioned to maintain an aerodynamic shape. The thickness dimensions of this portion of the blade are not sufficiently large to retain the weight pockets and their associated weighs, without adding significant reinforcement, which unacceptably adds weight to the blade.